Phase front plotting device



April 8,1950 H. IAMS PHASE FRONT PLDTTING DEVICE 3 Sheets-Sheet 1 FiledApril 18, 1947 /PAPER 0::- Wm:- UA/DER TEJT PAPER V///////////7/)/////INVENTOR. Harley Iams ATTORN EY April 18, 1950 H. IAMS PHASE FRONTPLOTTING DEVICE Filed April 18, 1947 3 Sheets-Sheet 2 7 I R m T 0 M m mM q MW ,8 m fl 0 4 r H H H J a m H 5 7 9 2 4 w MOS/MILE REC'OkD/A/GINVENTOR Iams ATTORNEY Ap 18, 1950 H. [AMS- PHASE FRONT PLOT'II/NGDEVICE 3 Sheets-Sheet 3 Filed April 18, 1947 I 7 Harl g f fiins ATTORNEY Patented Apr. 18, 1950 r PHASE mom PLOT'IING nnvrca Harley Iams,Princeton, N. J., assignor to Radio Corporation of America, acorporation of Delaware Application April 18, 1947, Serial No. 742,355

9 Claims. 3439-100) This invention relates to improvements in the art ofdetermining and depicting the behavior of ultra high frequency radiowaves, and particularly to apparatus for plotting phase fronts in aradio frequency field. Phase front diagrams are equivalent to picturesof radio waves, and are useful in studying the performance of antennas,radio lens systems, and the like. Other information, such as therefractive index of dielectric materials, may be obtained from phasefront dia- 'grams.

The term phase front as used herein is intended to mean a line extendinggenerally transversely to the direction of energy flow in a field,connecting points at which the time phase of electric vector of thefield is the same. A phase front diagram comprises one or more suchlines, each line being a locus of points of equal phase.

The invention will be described with reference to the accompanyingdrawings, wherein:

Figure 1 is a schematic outline drawing of a phase front plotting deviceembodying the present invention,

Figure 2 is a sectional elevation of a field probe and marker structureincluded in the system of Figure 1,

Figure 3 shows a modification of the system of Figure 1 in which thefield probe and marker are physically separate and are coupled togetherby a system of levers,

Figure 4 is a sectional elevation of a modified probe and marker,particularly adapted for recording on facsimile paper,

Figure 5 is a typical diagram produced by the system of Figure 1 usingthe marker device of Figure 2,

Figure 6 is a phase front diagram produced by the system of Figure 2using the marker device of Figure 4, and

Figure '7 is field intensity pattern. plotted by the system of Figures 1and 4, for comparison with the phase front diagram of Figure 6.

Refer to Figure 1. An oscillator I is connected by a wave guide 3 to thedevice to be tested, which is in the present example a horn radiator 5.A second wave guide 1 branches from the wave guide 3 and is connected toa rotary joint 9 of the type commonly used for coupling two relativelymovable waveguides. A third wave guide section II is connected betweenthe rotary joint 9 and a second rotary joint l3. The wave guide sectionII is provided with an attenuator l5 which may be in the form of a plateof poorly-conducting material movable into and out of the guide througha longitudinal slit.

A crystal detector I1 is coupled to and supported by the wave guide II.The output circuit of the detector I1 is coupled to an amplifier I. Anoutput meter 2| is provided in the output circuit of the amplifier IS.

A further wave guide section 23 is connected at one of its ends to thejoint It. The other end of the guide 23 carries a probe 25, which may beeither of the types shown more clearly in Figure 2 or Figure 4respectively. The lengths of the various wave guide sections are chosenso that the probe 25 is movable throughout the portion of the field ofthe device 5 which is of interest. A portion of wave guide 23 is splitand a clamp 24 is provided to vary the width of the guide. This permitsan adjustment of the phase of the signals reaching detector I! fromprobe 25. By such adjustment the recorded phase front can be made topass through any desired point.

Referring to Figure 2, the probe 25 comprises a coaxial transmissionline formed by a tube 2'! of conductive material which constitutes theouter conductor and a smaller tube 29 supported therein On insulatingbushing 33 and the metal bushing 3|. The inner conductor 29 extendswithin and across the wave guide 23. The lower end portion 35 of theinner conductor 29 extends beyond the outer conductor 21 and acts as acollector antenna. A rod 31 is supported slidably within the tubularinner conductor 29 and is provided with a sharp point 39 at the lowerend. The upper end of the rod 31 is provided with a knob or button 4|. Acompression spring I! surrounds the upper end of the rod 31, engagingthe button ll and the bushing 3| to urge the rod 31 upward.

In the operation of the described device a sheet 45 of paper or similarmaterial is supported in the field of the device '5, substantially inthe plane in which the phase front diagram is determined. The device 5is energized through the wave guide 3 in the oscillator l. Theoscillator i may be of the continuous wave type, or may be pulsed orotherwise modulated in order that the detector I! will provide an A.-C.signal suitable for amplification by an ordinary audio amplifier. Aportion of the output of the oscillator I is applied to the detector I'Ithrough the waveguide section II. The attenuator I5 is adjusted so thatthe amplitude of this energy is approximately equal to that picked up atthe probe 25 in the field of the radiator 5.

The probe is moved over the paper 45 to a point where the energyarriving at the detector I! from the probe 25 is either in phase ordegrees out of phase with that arriving at the detector I! through thewave guide section II. This condition is indicated by the meter 21 whichwill exhibit a maximum deflection when the two inputs to the detector I!are in phase or minimum deflection when they are out of phase. Eitherthe in phase or out of phase condition may be used toindicate a phasefront. Supposing the in phase condition is selected. The probe 25 isthen moved to a position which causes the meter ii to deflect to amaximum extent. At this point the button ll is pressed causing thepointed end 39 of the rod 31 to penetrate the paper 45.

The probe 25 is then moved to another reasonably nearby point whichagain provides maximum deflection of the meter 2|, and another mark ismade on the paper by the point 39. This process is continued point bypoint at sufliciently small intervals to establish the positions of oneor more phase fronts in the field picked up by the probe.

'The resulting appearance of the paper is illustrated in Figure 5, wherelines have been drawn connecting the points of equal phase. It will beobserved that the phase front lines in Figure appear to be curved moreor less about a common center point. This point is the effective centerof radiation of the horn 5. When the horn is used to illuminate a lensor reflector, this effective center should be placed at the focus, inorder that the sharpest possible beam shall be formed.

A substantially continuous record, rather than the point-by-pointdiagram of Figure 5, may be made by the modified probe and markerstructure shown in Figure 4. As in the device of Figure 2, the probeincludes a coaxial transmission line section with its inner conductor 49extending across the inside of the wave guide 23. The upper end portion5| of the conductor 49 extends beyond the upper end of the outerconductor 21. The marker is a rod 53 of conductive material supported on'an insulating block 55 which is secured to the wave guide 23 by abracket 51.

A roller 59 is provided on the bracket 51 to support the structure on asheet SI of currentsensitive paper like that used in facsimilerecorders. The paper 6| is spread on a flat metal plate 63. The lowerend of the rod 53 is pointed, and this point is maintained in contactwith the paper it. The rod 53 is connected by a wire 65 to one of theoutput terminals of the amplifier IS, the other output terminal beinggrounded to the plate 83.

with the device of Figure 4 incorporated in the system of Figure 1, theexposed portion 5| of the conductor 49 acts as a collector antenna. Itsoutput is mixed in the detector I! with energy taken directly from theoscillator I, and the resulting output from the detector is amplifiedand applied to the marker 53 and the plate '63. Current flowing throughthe paper 6| from the marker 53 to the plate 63 causes the paper 6| tochange color. Thus, when the collector is at a point where the signalarriving at the detector I! from the probe is in phase with thatarriving at the detector through the wave guide I I, the point on thepaper in contact with the marker 53 will be darkened. When the signalsarriving at the detector are out of phase, the paper will remain light.

The probe structure is moved back and forth like a paint brush to scanthe area which is of interest. The lines of motion need not conform tothe phase-front lines. The probe may be moved manually, or any suitablemechanism may be used for driving it automatically over successive linesacross the paper. The .resulting record is shown in Figure 6. Theinterpretation of the record is the same as that of the record shown inFigure 5.

If the wavelength of the energy used is too long to provide a completerecord on a conveniently small paper area, the probe and marker may beconnected by a pantograph linkage as shown in Figure 3. The probe ispreferably of the type shown in Figure 4, and is supported at the end ofthe wave guide 23. A pair of levers 81 and 89 are pivotally connected tothe wave guides H and 23 at points H and 13 respectively, and arepivoted together at the point 15. The marker I1 is supported at thepoint 15, and may be either of the type shown in Figure 2 or of the typeshown in Figure 4. The operation of the system is the same as thosealready described, except that the motions of the marker 11 are reducedwith respect to those of the probe 65, providing a record of smallerdimensions than the actual phase fronts.

Another useful application of the described systems is in themeasurement of refractive index of a dielectric material. This is doneby placing a sheet of the material between a radiator (for example, thehorn 5) and the probe, and measuring the resulting displacement of aphase front. The refractive index R is 1+S/T, where S is the phasedisplacement and T is the thickness of the sample. The dielectricconstant C is equal to R.

By disconnecting the wave guide H from the detector II, or closing theattenuator [5 to provide substantially complete cutoff, the system ofFigure 1 can be used to plot field intensity patterns instead of phasefront diagrams. The probe 25 marks points where the field intensity isthe same, as indicated by equal readings of the meter 2|. The same typeof record can be produced by an electrical marker like that of Figure 4;points of equal field intensity are of equal darkness. An example ofsuch a record is shown in Figure '7.

Variations of the structures shown here will be apparent to thoseskilled in the art. For some purposes small horns or open wave guidesmay be used for the pick-up probe. Concentric or parallel wire lines maybe used instead of the wave guides. When the detector is replaced by amicrophone the apparatus can be used to observe acoustic waves.

I claim as my invention:

1. A device for plotting phase fronts in a radiation field, including anenergy collector movable within said field, a detector, means connectingsaid collector to said detector, said connecting means being of constanteffective length, means providing reference energy like that of saidfield and of phase which is independent of the position of saidcollector, means applying said reference energy to said detector, andmeans indicating maxima and minima in the output of said detector; amarking device movable over a sheet of recording medium such as paper,and means mechanically connecting said marking device to said collectorelement to position said marking device in accordance with the positionof said collector.

2. A device for plotting phase fronts in a radiation field, including anenergy collector movable within said field, a detector, means connectingsaid collector to said detector, means providing reference energy likethat of said field and of phase which is independent of the position ofsaid collector, means applying said reference energy to said detector,and means indicating maxima and minima in the output of said detector; amarking device movable over a sheet of recording medium such as paper,and means to position said marking device in accordance with theposition of said collector.

3. A device as described in claim 1, with means for scanning a portionof space with said collector.-

4. A device for plotting phase fronts in a radiation field, including anenergy collector movable within said field, a detector, means connectingsaid collector to said detector, said connecting means being of constanteflective length, means providing reference energy like that of saidfield and of phase which is independent of the position of saidcollector, and means applying said reference energy to said detector; amarking device movable over a sheet of recording medium such as paperand responsive to output from said detector to mark said medium, andmeans mechanically connecting said marking device tosaid collectorelement to position said marking device in accordance with the positionof said collector.

5. A device for plotting phase fronts in a radiation field, including anenergy collector and means for moving said collector to scan said field,a detector, means connectingsaid collector to said detector, saidconnecting means being of constant efiectivc length, means providingreference energy like that of said field and of phase which isindependent of the position of said collector, and means app yin saidreference energy to said detector; a marking device movable over a sheetof recording medium such as paper and responsive to output from saiddetector to mark said medium, and means mechanically connecting saidmarking device to said collector element to position said marking devicein accordance with the position of said collector.

6. A device for plotting phase fronts in a radiation field, including anenergy collector probe movable within said held, a detector, means con-6 necting said collector to said detector, said connecting means beingof constant efiective length, means providing reference energy like thatof said field and of phase which is independent of the position of saidcollector, means applying said reference energy to said detector, andmeans indicating maxima and minima in the output of said detector; and amarking device substantially concentric with said probe and movabletherewith over a sheet of recording medium such as paper.

7. A device as described in claim 1, wherein said means applying saidreference energy to said detector includes an adjustable attenuator.

8. A device as described in claim 1. wherein said means connecting saidcollector to said detector includes a phase shifting device.

9. A recording device to produce a record on an element having a facefor receiving said record, and comprising a radio frequency antenna, ahollow. tubular conductor, and a marking device including a rodextending within said conductor and longitudinally movable therein, saidrod being electrically connected to said antenna and having an exposedstylus-like portion applied to said element face to make the recordthereon.

HARLEY IAMS.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS Number Name Date 1,525,177 Goldschmidt Feb. 3,1925 1,972,388 Mack Sept. 4, 1934 2,106,713 Bowen Feb. 1, 1938 2,106,771Southworth Feb. 1, 1938 2,202,634 Mack May 28, 1940 2,406,406 SandrettoAug. 27, 1946 2,407,267 Ginzton Sept. 10, 1946 2,415,807 Barrow Feb. 18,1947

